orthodontics vs orthodontia

orthodontics and orthodontia both are nouns.

Word	Noun	Adjective	Verb	Adverb
orthodontics	Yes	No	No	No
orthodontia	Yes	No	No	No

As nouns, orthodontics and orthodontia are synonyms defined as:

orthodontics and orthodontia: the branch of dentistry dealing with the prevention or correction of irregularities of the teeth

Other synonyms of orthodontics include dental orthopaedics, dental orthopedics, orthodonture.

orthodontics (noun)	orthodontia (noun)
the branch of dentistry dealing with the prevention or correction of irregularities of the teeth	the branch of dentistry dealing with the prevention or correction of irregularities of the teeth